1. Field of the Invention
The present invention relates to a private branch exchange system, and more particularly to an Internet protocol telephony exchange system.
2. Description of the Related Art
In these times, following the current trend of rapidly growing Internet technology, the need for various kinds of services is rapidly increasing and an IP-based network is also rapidly developing not only in the Internet performance aspect but also in the Internet service aspect. For instance, voice signal transmission over an IP network may be considered as one of a variety of services. A VoIP (Voice over Internet Protocol) supports such voice signal transmission over the IP network. The IP network is typically implemented in consideration of data transmission, but currently needs to be implemented in consideration of voice transmission as well as the data transmission.
Due to the aforementioned demands, integration between a universal legacy telecommunication and a VoIP is increasingly developing to enable the universal legacy telecommunication and the VoIP to interwork with a current communication network. The representative examples for this purpose are an IP-PBX (Internet Protocol-Private Branch Exchange) and an IP-Centrex, etc. Accordingly, a phone terminal usable in the IP network should be designed to perform the same operation as a prior PSTN (Public Switched Telephone Network) in the same format as the prior PSTN.
Presently, there are several kinds of common IP-phone protocols, that is, H.323 recommended by an ITU-T (International Telecommunication Union-Telecommunication) Standardization Sector, a media gateway control protocol (MGCP) used between a media gateway and a media gateway controller for controlling the media gateway and a SIP (Session Initiation Protocol) being multimedia telecommunication standards for data, voice, and video signals.
Typically, an IP network and a PSTN are spaced apart from each other, and terminals accessible to each network are controlled in different protocols and characteristics. For example, a terminal accessible to the PSTN may be an analog telephone, a digital telephone, and a MODEM (Modulator-Demodulator), etc. A terminal accessible to a trunk may be an E1/T1, a primary rate interface (PRI), a loop and a No. 7 signaling, etc. An IP terminal accessible to the IP network may be a H.323 terminal, a MGCP terminal, and a SIP terminal, etc. In order to perform voice transmission/reception using the IP terminal and an IP network, the IP terminal and the IP network should be connected to an IP line over a LAN (Local Area Network) and a gate keeper.
In order to establish communication between a subscriber of the IP network and a subscriber of the PSTN by enabling the IP network to interwork with the PSTN, at least one of many gateways is inevitably required, and an independent system configuration is also required to occupy such a gateway between the IP network and the PSTN. These requirements mean that the IP network and the PSTN respectively have an independent number system and an independent terminal management system. That is, the IP network and the PSTN are different in a number system and a terminal management system.
In the case where a common legacy terminal contained in a PSTN calls another common legacy terminal, it attempts to establish a call connection state by dialing a predetermined prefix according to a position (i.e., an intra-office call, a long-distance call, an international phone call, and a wired/wireless call) of a called party's terminal. However, in the case where the called party's terminal is an IP terminal, a corresponding legacy terminal needs to dial a specific prefix occupying a gateway connected to an exchange system in such a way that the legacy terminal can perform a call control.
The IP terminal connected to the IP network dials a predetermined prefix depending on a counterpart terminal's position (i.e., intra-office area or other area). In case of attempting a call for a PSTN, the IP terminal needs to dial a prefix used for occupying a gateway connected to an exchange system controlling a counterpart terminal.
However, the aforesaid conventional technique establishes an independent call control mode between a PSTN's terminal and an IP network's terminal, because the PSTN's terminal and the IP network's terminal are respectively designed to have independent systems. As a result, the PSTN's terminal and the IP network's terminal perform different functions independently from each other, so that it is difficult to accomplish integration of IP terminals within either a zone using a prior PSTN or one building. In other words, in case of implementing an IP-based PBX, the conventional technique cannot control a call of an IP terminal in such a PBX in the same manner as an extension subscriber, so that it cannot use a plurality of extension functions provided in the PBX.